1. Field of the Invention
This invention relates to tin oxide coatings, and, more particularly, to a chemical vapor deposition method of producing transparent, haze-free tin oxide coatings on glass.
2. Description of the Prior Art
Tin oxide is widely used as a coating material in optical instruments. For example, U.S. Pat. No. 4,497,700 describes the use of tin oxide as an anti-reflective coating in a multi-layer optical filter. This tin oxide coating is required to be transparent and haze-free in order to avoid interference with the optical performance of the device. Similarly, Gordon, in U.S. Pat. Nos. 4,187,336 and 4,206,252, uses a tin oxide coating to reduce or cancel iridescence in glass window structures. While such tin oxide coatings function effectively for the purposes intended, they introduce haze into the system unless formed under very restrictive and disadvantageous deposition conditions.
A number of patents are directed to reducing haze in tin oxide coatings, see e.g. U.S. Pat. Nos. 2,567,331; 2,614,944; 2,617,741; 3,677,814; 3,759,743; 4,187,336; and 4,329,379. These patents teach the avoidance of tin tetrachloride, or any other similar compound containing a halide, which can produce an acid vapor at the hot glass surface. In the event a halide-containing compound is used, it is suggested in these disclosures, that an additive, such as hydrazine, be included in the coating composition, or that an undercoat layer of a metal oxide, for example, silicon dioxide, precede the tin oxide coating.
Accordingly, it is an object of this invention to provide a chemical vapor deposition method of producing transparent, haze-free tin oxide coatings.
Another object of this invention is to provide a chemical vapor deposition method of producing haze-free tin oxide coatings on a substrate such as glass in which the coating is produced rapidly at an elevated substrate temperature using a non-corrosive, non-toxic liquid organotin compound.
Still another object of the invention is to provide such a transparent, haze-free tin oxide coating without requiring an additive in the coating composition, or an undercoat layer.